The USSD service is a new interactive data service based on a Global System for Mobile Communication (GSM) network. A user can enter a service access code custom-made by a network in advance through a Mobile Station (MS) keypad, for example, “108#”, and then press a “transmitting key” so that an instruction can be transmitted to the network. The network returns to a main menu according to the instruction transmitted by the user, the user can select an next operation according to a prompt of the main menu, and the network returns to the next level of menu or content according to the selection of the user, thereby providing the USSD service needed by the user.
In the GSM network, both the USSD service and a Short Message Service (SMS) transmit data through a signaling channel of the network. The USSD service uses a Stand-alone Dedicated Control Channel (SDCCH) in a session state, and uses a Fast Associated Control Channel (FACCH) in a non-session state. The difference between the USSD service and the SMS is in that the SMS adopts a store and forward mode and the USSD service adopts a session-oriented mode, and the USSD service has characteristics such as a fast response speed, strong interaction capacity, high reliability, etc., and is suitable for providing services of payment type and transaction type for users, for example, account query, recharge, transfer accounts, report the loss, etc.
In the CDMA network, due to the limitation of the existing CDMA network protocol, the USSD service cannot be implemented, thereby it is impossible to provide users with the USSD services such as account query, recharge, etc. In the existing CDMA network, some mobile intelligent network services, such as Pre-Paid Charging (PPC) service, implements some USSD functions through a short number access management mode of USSD like; however, real-time message interaction cannot be performed between the user and the network, and thus, there is a large limitation, and portability and scalability are poor.